[amsat-bb] Splitter for receiving system?

Mark L. Hammond marklhammond at gmail.com
Fri Feb 6 22:51:16 UTC 2015

Thanks everybody for the great help.  I didn't describe my setup or goals
very well...but lots of ideas coming in.

I have multiple SDRs in the shack now.  I have a 2M array with low
noise/high gain preamp and 70cm array with low noise/high gain preamp that
I use for receive only (mast mount preamps, externally powered).    So, my
goal is any band with any SDR, no switching or cables.  Even 2 SDRs, same
band, same time...so here is what I envision:

I have separate feedlines coming into the shack--one for 2M one for 70cm.
Tie them together via a single diplexer.  Then, the single diplexer output
(carrying both 2M and 70cm) going into a splitter with multiple
outputs--going to FCDPP, Airspy, whatever...with a single split, it's 3dB.

The easy and cheapest solution had occurred to me---which is use a
cable/satellite TV splitter (I know, 75 ohms).  But a good idea from one of
you was to get the "variable amplified" version from RadioShack or
wherever.    I was thinking something more "elegant" at 50 ohms might be
worth while.

I'll probably try to the TV splitter and see how it works and if the loss
is OK.  Shouldn't be bad, given the preamps.

Anyhow, fun to chat about--thanks for all the private and public
responses.  Once I get a bit more time, I'll try to summarize some other
suggests a little better.


Mark N8MH

On Fri, Feb 6, 2015 at 10:30 AM, Howie DeFelice <howied231 at hotmail.com>

> Hi Mark, no matter what you use you will lose 3 db + the splitter
> insertion loss. If you are putting the splitter after a LNA, then the added
> loss is usually not important. However, if you are putting the splitter
> directly between the antenna and your receiver the loss of the splitter
> will add directly to the receiver noise figure, which in weak signal work
> is the real difference between hearing and not hearing a signal.
> If you can afford the 3+ dB increase in system noise figure, a plain old
> TV splitter is actually not bad. The outdoor variety are water tight,
> F-connectors are pretty good at UHF (in some ways better than a BNC).  If
> it's RX only, RG-6 is low loss, inexpensive and the slight mis-match is not
> that significant.
> If noise figure is important, a low gain, low noise figure amp before the
> splitter (which can be turned around and used as a combiner) is a good idea.
> Mini-circuits are great components and have a great variety of quality
> RF/IF components. The only problem is that their distribution network is
> limited and unless you find a retail source that has what you want getting
> parts can be a little difficult .... and you will start getting called by
> the "area rep" wanting to know how many hundred you will be needing every
> few months :) That said, they HAVE been accomodating when I needed
> something that wasn't available through distribution.
> - Howie, AB2S
> > Date: Fri, 6 Feb 2015 08:00:04 -0500
> > From: marklhammond at gmail.com
> > To: amsat-bb at amsat.org
> > Subject: [amsat-bb] Splitter for receiving system?
> >
> > Hello All,
> >
> > I am really wishing for a "splitter" for my receiving system, good for
> both
> > 2M and 70cm (so say, 144-450MHz or so.)
> >
> > Any suggestions? I really don't to lose 3dB in the process, but fear the
> > only way to avoid that is some powered/amplified system. I recall such a
> > device, but cannot for the life of me think where or the possible source.
> > I do not need to xmit through it; receive only. Also, I do not need to
> > pass 12V to power preamps, etc. So, just a low loss splitter good for 2M
> > and 70cm. SMA, BNC, N connectors--any will work in my shack.
> >
> > Do folks refer to these as splitters? Combiners? Power splitters? I know
> > about Mini Circuits--that's a sensory overload of stuff to pick through
> :)
> >
> > Any pointers to sources or such devices will be welcomed!
> >
> >
> >
> > Thanks---
> >
> > --
> > Mark L. Hammond [N8MH]
> > _______________________________________________
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> Opinions expressed
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Mark L. Hammond [N8MH]

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